Foam producing apparatus



April 1960 H. E. BEDFORD ETAL 2,934,149

FOAM PRODUCING APPARATUS 4 Sheets-Sheet 1 Filed llay 9, 1955 In uentors Attorneys April 26, 1960 H. E. BEDFORD ETAL FOAM PRODUCING APPARATUS 4 Sheets-Shet 2 Filed May 9. 1955 N. wa

mw Q Q T A ttorneys April 1960 H. E. BEDFORD ET AL 4,

FOAM PRODUCING APPARATUS Filed May 9, 1955 4 Sheets-Sheet 3 %M4 By A tlorneys April 26, 1960 H. E. BEDFORD EIAL 2,934,149

FOAM PRODUCING APPARATUS Filed May 9, 1955 4 sheets-sheet Inventors Hon 419p 5W 650M190) 77/0/1/75 W/vywvs/ovn;

A ttorneys FOAM PRODUCING APPARATUS Howard Edwin Bedford and Thomas Anthony Henshaw, Brenfiord, England, assignors to The Pyrene Company Limited, Brentford, England Application May 9, 1955, erial No. 507,039

Claims priority, application Great Britain May 13, 1954 11 Claims. (Ci. 169-15) This invention relates to apparatus for the production of mechanical foam in a generator of the injector type for fire-fighting purposes. It is primarily applicable to apparatus mounted on a vehicle which serves as a crash tender on an airfield.

It is well known that injector foam generators can be broadly divided into two types, namely forcing and non-forcing. In both types there is at least one orifice through which liquid is caused to emerge as a jet into a foam tube. In the non-forcing type, the air required for the production of foam is entrained by one or more jets of liquid from the atmosphere through an opening or openings which impose no restriction on the amount of air so entrained. In the forcing type of generator, the energy in the jet or jets is largely maintained by restricting the diameter of the foam tube and thus the amount of air which can be entrained. Thus air can be drawn in from the atmosphere or supplied under pressure. Generators of the forcing type may be defined as those which produce foam under pressure high enough for the foam to be delivered through a hose 4 inches in diameter and at least 60 feet long or against any equivalent back pressure; if there is no such back pressure then the foam will be delivered as a jet over a substantial distance.

In a crash tender it is not only necessary to overcome fairly considerable back pressure but also to project the foam over a substantial distance. Moreover, it is further required that the expansion, i.e. the ratio of the volume of foam to the volume of water used, should be high. In addition, on a crash tender the weight of the equipment required to deliver the water under considerable pressure to the foam generator must be low. If the air is simply drawn in from the atmosphere by suction, as is well known in the production of foam, then the necessary expansion cannot be obtained. Accordingly some air must be supplied under pressure, and the weight and size of the equipment for this must also be low.

A crash tender commonly carries its own supply of water and foam-stabilizing solution. The maximum use must be made of these, and this is another reason why the expansion ratio must be high.

Yet another requirement is that the generator shall be able to supply various amounts of foam per minute, since one large generator may be mounted to supply foam to a plurality of lines and only some of these may be required for dealing with a particular fire.

An object of this invention is to provide apparatus on a crash tender satisfying all the requirements.

Another object of the invention is to enable foam of equal quality to be produced at difierent outputs.

A further object of the invention is to provide a variable generator of the forcing type.

A still further object is to provide means for simultaneously delivering air and liquid to a generator in a constant ratio but at varying rates of flow.

Yet another object is to enable an apparatus to deliver 2,934,149 Patented Apr. 26, 1960 varying amounts of foam of equal quality under a single control.

Our invention will be most readily understood by reference to the annexed drawings, in which Figure 1 is an isometric view of the apparatus for a crash tender, some parts being shown detached for the sake of clarity;

Figure 2 is an elevation of,

Figure 3 is a plan of, and

Figure 4 is a longitudinal section through the generator and associated parts.

Referring first to Figure 1 the crash tender is a vehicle carrying a water tank 1 and a tank 2 containing a solution of a foam-stabilizing compound. The shaft of the engine of the vehicle can be connected through a clutch to drive the shaft of a blower 7 of the Rootes type which supplies air from the atmosphere to a foam generator 8 of the injector type. A centrifugal pump 9 is directly coupled to the shaft of the blower 7 through a coupling 6 and draws water from the tank 1 and delivers the water to the generator 8 at a rate dependent on the engine speed. Foam-stabilizing solution is drawn from the tank 2 by water passing through an inductor 10 and also delivered to the generator. The foam formed in the generator passes through a foam tube 11 to several foam lines, namely a pipe 12 leading to a projector 13 and also to two pipes and having connections to which foam hose pipes can be attached, two of which are shown at 14 and 15.

Referring now to Figures 1 to 4, this tank 1 can be charged and the pump 9 primed through pipes 76 and 77 respectively. In Figure 1 the generator 8 and associated parts are shown detached, their connections to the main body of the apparatus being indicated by dotted lines.

In order to maintain the efficiency of a generator under varying rates of flow of liquid it is important to maintain the pressure at which the liquid is supplied to the jet at a predetermined value. The pump 9 can be positively driven at different speeds by altering the engine speed, and so can supply liquid to the generator under constant pressure. An important feature of the invention is that the rate of flow of the liquid is controlled by a valve member which obturates the orifice in the generator to a greater or lesser extent.

In the construction shown the generator 8 comprises a casing 16 to which water is forced through a pipe 17 by the pump 9 and passes through an orifice 18 in a flange 19 on the casing. A valve device 20 includes a needle valve member 21 with a substantially pear-shaped head similar to the well-known Doble needle which can enter the orifice 18 and obturate it; The head of the needle is so large that when it is inserted to the fullest extent into the orifice 18 it closes it completely and acts as a shut-off valve for the water supply. This is advantageous in that it renders unnecessary the provision of a separate valve on the discharge side of the pump.

The valve device 20 has a spindle 38 which is small in diameter in relation to the needle head so as to prevent excessively large forces due to the water pressure acting to open the orifice when the water is flowing. It is found that by keeping the spindle small the force required to hold the needle at a given setting may be only 20 lbs. even when using a water supply at lbs. per square inch.

As shown, the needle member 21 and the inlet side of the orifice are streamlined in order to make velocity of the water the maximum at the pressure available by reducing turbulence to a minimum at the approach to the orifice.

The water issues from the orifice as a jet into a casing 22 which opens into the foam tube 11.

The blower 7 draws in air from the atmosphere through a silencer and filter 29 and an intake pipe 30 and delivers the air into a pipe 75 containing a non-return valve 74. The pipe 75 leads to the casing 22 so that air under pressure is supplied to thejet of water and foam-stabilizing solution. The air and jet pass together along the tube 11, forming foam in the process.

It will be seen that the air is delivered to the space around the jet entering the casing 22 and is entrained by the jet, but is itself supplied under a positive pressure. This should be at least pounds per square inch. If the pressure is higher than 15 pounds per square inch the sustained production of the necessary large volume of air (which in a crash tender may be 600 cubic feet per minute measured at atmospheric pressure) requires either a two-stage blower of the Rootes type or a positive displacement blower, both of which introduce mechanical complications.

We have found that a single-stage blower of the Rootes or equivalent type and of a convenient size, such as that shown at 7, can supply air in the required volume and at pressures within the range of 5 to 15 pounds per square inch when it is rotating at the same speed as a centrifugal pump, such as that shown at 9, which will deliver the amount of water required for the foam. The speed at which the blower and pump rotate is such that they may both be directly driven by the engine of the crash tender, so that no gearing is required in the drive to the blower or the pump.

The pressure under which the water is delivered by the pump 9 should be at least 80 pounds per square inch, and preferably is in the range of 120 to 150 pounds per square inch. it will be seen that this is very high in relation to the pressure under which the air. for the foam is supplied and yet that pressure is itself high in relation to the atmospheric pressure. This last feature leads to the desired high expansion, since if the air is merely drawn in under atmospheric pressure the expansion may be only 6 or 7, whereas if it is delivered under a pressure of about 10 pounds per square inch the expansion may be 14 or even more.

It is easily possible to control the speed of the blower and pump so that they supply air and liquid respectively at desired pressures. It is necessary, moreover, to control the rate of supply of liquid and air in accordance with the number of delivery lines actively supplying foam. The rate of supply of liquid is controlled by varying the total cross-sectional area of the jet orifice 18 of the generator by the valve device 20.

Although the speed of the blower is reduced with that of the pump, it is not feasible to provide a blower and pump which deliver air and liquid in the optimum ratio at all speeds of the engine shaft. Rather, the blower tends at reduced speeds to deliver more air than is required. To maintain the ratio at the optimum the valve device 20 is arranged to control the liquid and air simultaneously.

To this end, in the apparatus shown, a pipe 31 branches from the pipe 75 and leads to a casing 32 which is aligned with the casings 22 and 16 and joined to the casing 16 by an open frame 33. The casing 32 has a port 34- leading to an air-discharge pipe 35 and the tail end of the valve device 26 works in this casing. The pipe 31 is in fact a pipe along which air can bleed oif when the generator is not working to full capacity, and when the generator is at full capacity the entry of air into the casing 32 is prevented by a mushroom valve member 35 carried by the stem 38 of the valve device 20, which closes one end of the casing. The stem 33 makes a close fit in a re-entrant part 39 of the casing and thus prevents leakage of air from the casing. The part of the casing around the valve member 36 flares, as shown at 37, and when the valve device 20 moves axially the annular space around the valve member 36 varies in area, and so the air flow from the pipe 31 through the casing to the discharge pipe 35 is throttled to a greater or less extent. it will be seen that as the needle valve 21 is withdrawn from the orifice 18 to increase the size of the orifice for the passage of liquid, so is the air flow through the casing 32 throttled and thus more air is forced to flow from the pipe 75 into the casing 22. The ratio of air to liquid is thus maintained substantially constant.

The valve member 36 and the flaring part 37 are designed so that only enough air is allowed to escape to atmosphere to reduce the pressure of the air supply to the required value, normally 5 to 12 lbs. per square inch.

Although the liquid pumped to the generator 8 may be a dilute solution of foam-stabilizing compound stored ready for use, it is preferred to induce the foam-stabilizing compound into a water stream flowing to the generator.

In the apparatus shown, the water supplied to the casing 16 contains foam-stabilizing solution induced from the tank 2 through a pipe 24 by the inductor 10 into water passed through a pipe 23 from the pipe 17.

The mixture of water and foam-stabilizing solution produced in the inductor flows through a pipe 27 which joins a main suction pipe 28 leading from the tank 1 to the pump 9. Thus foam-stabilizing solution is continuously mixed with the water flowing in the pipe 17.

It is necessary not only to vary the rate of fiow of air, but also the rate of induction of the foam-stabilizing compound when the rate of flow of water is changed. To vary the rate of induction the valve device 20 is mechanically connected to the throat member 26 of the inductor. The valve spindle 38 is made in two parts, each having a threaded end, and the two threaded ends screw into a block 40 which lies within the open frame 33. The block 40 carries a pin engaged in a slot 71 at the end of an arm 72 rigid with a spindle 44 mounted in the frame 33. A bell-crank having arms 43 and 45 is also rigid with the spindle 44. The length of the arm 43 is adjustable by a pin-and-slot connection 73. The end of the arm 43 is pivoted at 42 to a connecting rod 49. The arm 45 of the bell-crank serves as a handle or operating lever, and when it is rocked the block 40 causes the valve spindle 38 to move axially with relative movement of the pin 41 and the slot 71.

The connecting rod 49 is adjustable in length and is pivoted toa crank 50. This crank is so connected to the throat member 26 of the inductor in the manner described in detail in application Serial No. $02,173 that rocking of the crank produces axial movement of the throat member and thus varies the rate of induction of the foam-stabilizing compound. In operation control is most conveniently effected from the driving cab of the crash tender. Accordingly, a remote-control cable 52 is connected to the arm 45 of the bell-crank and run toward the cab as seen in Figure 1.

Hoses 75 feet long are connected to the pipes 14 and 15. In flowing through these pipes the quality of the foam is improved by the frictional resistance, as is well known. To improve the foam similarly in the much shorter pipe 12 leading to the projector 13 a gauze is inserted in a wide part of the pipe 12.

If on arriving at a burning crashed aircraft the driver finds that he must use the projector 13 and the hose pipes connected to the pipes 14 and 15, he moves the valve device 20 so as to give maximum flow of water, maximum induction of foam-stabilizing compound and com-.

plete cut-off of air from the casing 32 by the valve member 36. If the engine is running at full operating speed, the blower and pump will start and foam will be produced at the maximum rate. The full operating speed is that which will give a water pressure of lbs. per

square inch as determined by observation of a pressure gauge connected to an opening 54 in the casing 16.

Suppose now that the fire is partly extinguished and the projector can be cut oif. One of the firemen closes a valve 53 in the pipe 12, and the man in the cab moves the arm 45 through the cable 52. At the same time he reduces the engine speed to that required to maintain the same Water pressure in the casing 16. The speed of both the blower and the pump are reduced with the engine speed. In practice the blower and pump can be so designed that they give the required amounts of liquid and air when running at full speed, but by their nature they Will not deliver water and air in the optimum ratios required at lower speed. Rather the blower then tends to deliver too much air. It is for this reason that provision is made for bleeding away surplus air through the discharge pipe 35.

It is desirable to calibrate the settings of the main control lever 45 and the inductor 10. For this purpose a disc 80 is fixed to the spindle 44 and is provided with markings which register with a mark on a member 55 fixed to the frame 33, and a similar disc 56 is fixed to a spindle 57 rigid with the crank 50 and carries markings which register with a mark on a member 58 rigid with the casing of the inductor 10.

As an example in one apparatus made as shown in the drawings, 2200 gallons of foam per minute were thrown 110 feet with the apparatus adjusted to give a water flow of 180 gallons per minute at 130 lbs. per square inch in the casing 16. The air pressure in the casing 22 was 12.2 lbs. per square inch and the resultant expansion ratio was 13.

The water pressure and rate of flow and the air pressure remained the same when the two hoses, each 4 inches in diameter and 75 feet long with a 3-inch nozzle, were used instead of the projector. 2600 gallons of foam per minute were thrown 75 feet at an expansion ratio of 14.5.

When the projector and one hose were used together With the same Water and air pressures, the rate of flow of water was increased to 280 gallons per minute to give 3500 gallons of foam per minute at an expansion ratio of 12.5.

It will be observed that the pressure of the foam produced by the forcing generator was not only enough to overcome the back pressure of the two hoses, and almost the same back pressure imposed by the projector and the gauze-containing pipe 12 leading to it, but also in each case to project the foam over a considerable distance.

We claim:

1. Fire fighting apparatus for producing constant quality mechanical foam at varying output, comprising an injector generator of the forcing type with at least one jet orifice, means for supplying substantially constant pressure water containing a predetermined amount of foam stabilizing solution to said orifice to produce a jet emerging therefrom, means for supplying air under pressure to the space around said jet, a valve device cooperating with said orfice to obturate it to a variable extent, means communicating with said air supplying means for withdrawing a portion of the air being supplied to said space, and means connected to said valve device for controlling the extent of said portion of air withdrawn from said air supplying means in opposing relation to the obturation of said orifice.

2. Fire fighting apparatus according to claim 1 wherein the means for withdrawing a portion of the air being supplied to the space around the jet includes an exhaust passage communicating with the air supplying means and having a valve therein.

3. Fire fighting apparatus according to claim 2 wherein the means for controlling the extent of the portion of air Withdrawn from the air supplying means includes a valve closure member connected to the valve device and cooperating with the valve in the exhaust passage to obturate it to a variable extent in opposing relation to the obturation of the orifice.

4. Fire fighting apparatus according to claim 3 Wherein the valve device comprises an axially movable spindle having a valve head cooperating with the orifice to obturate it to a variable extent with movement of the spindle.

5. Fire fighting apparatus according to claim 4 wherein the valve closure member connected to the valve device is a valve tail on the spindle cooperating with the valve in the exhaust passage to obturate it to a variable extent in opposing relation to the obturation of the orifice with movement of the spindle.

6. Fire fighting apparatus according to claim 5 wherein the valve head is adapted to completely close the jet orifice.

7. Fire fighting apparatus according to claim 6 wherein the valve tail is adapted to completely close the valve in the exhaust passage.

8. Fire fighting apparatus according to claim .7 wherein the valve head is substantially pear-shaped.

9. Fire fighting apparatus according to claim 1 wherein the means for supplying water containing a predetermined amount of foam-stabilizing solution under substantially constant pressure to the orifice to produce a jet emerging therefrom includes an inductor for inducing foam-stabilizing solution into a stream of water.

10. Fire fighting apparatus according to claim 9 wherein the inductor includes a movable part operatively connected with the valve device for controlling the rate of induction of solution such that the proportion of solution in the stream of water is maintained substantially constant.

11. Fire fighting apparatus according to claim 1 further comprising at least two delivery lines connected to receive foam from the generator and means for controlling the flow of foam from the generator to one of the lines independent of flow to at least one other of the lines.

References Cited in the file of this patent UNITED STATES PATENTS 401,452 Nash Apr. 16, 1889 808,711 Adreon et al. Jan. 2, 1906 2,004,281 Henkel et al June 11, 1935 2,130,745 Rosenbauer Sept. 20, 1938 2,218,294 Muller Oct. 15, 1940 2,532,986 Bedford et al Dec. 5, 1950 2,611,439 Faulkner Sept. 23, 1952 2,769,500 Cliiford Nov. 6, 1956 

